1. Field of the Invention
The present invention relates to an arrangement including a method and an apparatus for controlling the air-fuel ratio in an internal combusttion engine having an exhaust gas recirculation system, and more particularly to a system for computing an amount of fuel to be injected into an engine through a speed-density system or a throttle-speed system.
2. Description of the Prior Art
There is known an internal combustion engine having air-fuel ratio controlled by a speed-density system which determines a basic amount of fuel to be injected on the basis of intake air pressure and engine speed (RPM). The internal combustion engine has a passage for recirculating an exhaust gas from an exhaust manifold to an intake manifold. In purifying the exhaust gas with such exhaust gas recirculation (EGR) control, the pressure in the air intake tube is determined by air drawn and a recirculated gas. Where the amount of fuel to be injected is determined using the pressure in the air intake tube directly as a parameter, the air-fuel ratio tends to render the air-fuel mixture rich.
To avoid the above drawback, there is disclosed in Japanese Laid-Open Patent Publication No. 48-27130 a system for reducing the amount of fuel to be injected dependent upon exhaust gas recirculation. This reference suggests any that it is appropriate to reduce a fuel injection amount when exhaust gas recirculation is being carried out. Fuel injection amount is determined only by intake manifold pressure and engine RPM. When exhaust gas is recirculated, the intake manifold pressure increase. Thus fuel injection amounts controlled indirectly. No sufficient study has been made of a method of setting both the amount of the recirculated gas dependent on the engine condition and while simultaneously controlling the amount of fuel to be injected at that time. The engine RPM and torque may vary and harmful components tend to be discharged with the exhaust gas when the air-fuel ratio is changed in an EGR control mode.